As black: the London System With Colors Reversed

The only reason I can see is answering 6.c4 with 6...Bb4+, when the "natural reaction" 7.Nc3? loses to 7...Qa5.

But then, I do not see why white has to hurry pushing c2-c4.

I’m not saying that the position is winning for black, but black’s game is very comfortable. Your pieces are coordinated and both queenside and kingside attacks are possible. Plus, don’t downplay the fact that it’s very disruptive to the plans of many Nimzo-Larsen players go for. With best play white is equal, but they have to be moves that they usually don’t like to make. For instance, if you retreat the bishop to d6, white’s best move in some positions is often to try to trade it off with Ba3, but I have never seen an N-L player willingly part with that bishop.

Edit: to be fair, though, you're an IM and I stink. The opponents you face are much more likely to be adaptive to the needs of the position than the players that I face, who are much more likely to stick with their usual plans even if they aren't the best.

Stockfish may approve but in general, GM commentators disapprove of a premature c3 or c6 in related openings, so Pfren's reaction is no surprise.

Correct me if I'm wrong, but in the specific position after 1.b3 d5 2.Bb2 Nf6 3.e3 Bf5 4.Nf3 e6 5.d4, isn't 5...c6 just one of several reasonable moves? As I see it, it defines black's approach to the question of the centre, and in broad strokes the coming middlegame. 5...c5 is also possible, but that leads to a different middlegame with different possibilities for both players. And of course, it is also possible to defer any commitment for the moment with a move such as ...Be7 or ...Bd6 or ...Nd7 or maybe even ...a6. A lot of moves are possible; although I have a lot of respect for stockfish, I don't think it's fraction of a centipawn favourite is the absolute last word to be said here. It's a matter of choosing the middlegame you want to play, isn't it? 

Masters who can handle subtle maneuvers and well-timed pawn beaks might well be able to make a lot of hay out of the solid triangle e6-d5-c6. Me, I'm not so skilled, I have trouble finding anything useful and active to do in such positions. (Yes, Pfren, you've said it before, and you're right. There are no boring positions, only boring players. Mea culpa, I'm a boring player) I would prefer (and this is just my personal preference) to introduce a bit of central tension by playing a quick ...c5, or maybe preparing ...c5 with Nbd7 first.  (Hmmm, where does the N belong in such positions, d7 or c6? Or is there no one correct answer to that question?)

Seems there are a lot of questions in this specific position, and this is just one example that NikkiLikeChikki gives of an opening that black might use this set-up in response to. White's first 5 moves are certainly not forced. I think it's a good example, because it introduces the issue of flexibility in planning. Sooner or later, both players will have to make decisions about the centre and the shape of the coming middlegame. How long does one wait and see, how soon does one stop making "this is my set-up" moves and start operations?

Maybe, but if you look at the stem position after c6 I think it's pretty obvious that it's black who is playing for advantage. There are no weaknesses and plenty of piece coordination. The position has been reached 125 times in 2500 rated games, and black has won 56% of the time and white only 33%.

I played someone several hundred points higher than myself in a 30|20 to a draw from this position and only because I stupidly allowed a perpetual. Otherwise I was better. I have had a lot of luck with it. It's not a panacea by any means, but it's a solid structure to fight against the rare Nimzo-Larsen opening. I have no desire to learn theory against rare openings if I don't have to.

I'm in my early sixties, and of course I cannot play like an IM now. Say some 150 rating points lower that the limit, and they will be more and more.

5. d4 is without doubt a bad move in this Nimzo-Larsen. At this point, I don't care how many GMs may play it. It's a bad move. ...c5 would be a bad response which would make d4 into a much better move. That's the only reason I can think of to play it .... but even so, c6 is unnecessary.

5.d4 is Stockfish's #1 choice in the position and the move that gives white the best chance of winning in the Master game database. 5.c4 wins 24% and 5.d4 wins 34%. 5.c4 is much more likely to draw, though. I won't argue about the minutia, but it's clearly not objectively bad, it just doesn't conform to your predispositions.

I think you mean that 5. d4 has the highest win rate among masters but that doesn't make it the best move. It makes it the move that most players, playing black, slip up against, possibly because they over-react to a bad move which blocks in white's bishop.

So you misunderstand. It's objectively bad. There's no doubt about that; but win-lose ratio isn't an objective measure of a move but a practical one.

If you say so. I just think that if Stockfish says it's best and white wins with it the most, then it's not objectively bad. Notice that I did not say that it was the best move, I just presented a couple of nuggets and said it wasn't bad. The definition of objective is that it's not infuenced by personal opinion or feelings, and to my knowledge Stockfish doesn't any feelings about anything. You don't like it—that's clear and that's fine. I won't argue with you.

Stockfish is only really any good at endings though. It can't assess a dull openings position where it's out of book. In the variation of the QGD where black plays h6 and then if the bishop retreats, b6, sometimes white delays taking on d5, which fixes the central pawns. Black can also delay Bb7. The point is that when the central pawns are fixed, the B is buried at b7 and it would prefer e6.

This is a similar type of position. So who plays 1. b3 and when do they play it? You can't assess a move's "objective value" according to a win/lose rate unless you have full stats on who the sets of players are who play the black and white sides and what their ratings are, when the opening tends to be played etc. So that's two sets of evidence that d4 is the best move, neither of which is sound.

Not quite. A dictionary may try to do something like that though. Roughly speaking, "objective" means "real", "actual", "as exists" etc. But in any case, the only evidence we have of what exists is via our perceptions, interpretations of perceptions and judgement. The only practical meaning we can have of "objective" is "related to an attempt to bring in all the evidence". That's all it can be .... just a subjective attempt to be objective and nothing more.

Also, like all chess engines, SF is programmed by humans.